A. Field of Invention
The present invention relates generally to a device for closing and locking two portions of a mold in diecasting or injection molding machines. More specifically, the invention relates to a mold closing device of the type that includes a fixed mold carrier plate, a fixed end plate, and a movable mold carrier plate that can be displaced from an open to a closed position between the fixed mold carrier plate and the fixed end plate through the use of a piston-cylinder unit that acts on the movable mold carrier plate.
In addition, the invention generally relates to an improvement in mold closing devices of the described type that also include a pressure plate to lock the two parts of the mold together. The pressure plate is carried on a swivel arm that is rotably mounted on one of the shafts that support the fixed mold carrier plate; it may alternately be moved between and from between the piston-cylinder unit and the movable mold carrier plate.
In the present invention, the swivel arm and its pivot bearing are carried on a shaft in such a way that the pressure plate has a limited displacement range against a spring tension. That displacement range is shorter than the stroke of the piston in its cylinder. The swivel arm is pivoted against a pressurized cylinder that is supported from a neighboring shaft. For spanning the distance between the movable mold carrier plate and the piston-cylinder unit, a gradually adjustable longitudinal distance-determining member is provided.
B. Description of the Prior Art
Mold closing devices of the general type described here are known in the prior art. See for example, German Pat. Nos. 11 27 069 and 21 09 957 (hereafter the No., '069 and No. '957 patents). For example, the inward and outward pivoting of the pressure plate in the mold closing device of the No. '069 patent is established in a relatively simple way: the pivot bearing of the swivel arm is immovably located on one of the shafts and the pressure plate is rigidly attached to the free end of the swivel arm.
This arrangement, however, has several disadvantages. For example, the faultless inward and outward pivoting of the pressure plate is not reliably assured. The swivel arm remains in a fixed position on the shaft and the pressure plate hangs in unbalanced suspension on the swivel arm. To open the mold, the pressure on the piston is released so that it returns to its initial unengaged position. During this process, firm contact between the pressure plate and the movable carrier plate ceases and a gap appears between the piston and the pressure plate held by the swivel arm. When the pressure plate is swung out of this position, it glides along the movable mold carrier plate; however, when the pressure plate is subsequently swung inwards, it may strike the movable mold carrier plate in an undesirable way. Jamming may occur and the pressure plate and the movable mold carrier plate may be damaged. This disadvantage arises because the displacable swivel arm does not exactly retain the same orientation throughout its outward swing and because the swivel arm may become somewhat twisted on its shaft from the unbalanced suspension of the pressure plate from its pivot bearing. This disadvantage can be eliminated if a more uniform weight distribution is achieved. However, in such an arrangement there may still arise a small deflection of the shaft that carries the swivel arm in the region between the end plate and the movable mold carrier plate.
Another disadvantage of the prior art mold closing and locking devices of the type described here arises from the twisting of the pivot bearing on its shaft that may occur with the displacement of the swivel arm carrying the pressure plate when the piston is activated. This situation may result in damage to the bearing faces and thereby a loosening of the bearing so that accurate preservation of the pressure plate perpendicular to the shaft is not reliably insured. Extended use might cause the swivel plane to shift obliquely with respect to the plane of the movable mold carrier plate, thereby impairing the operating ability of the entire mold closing device.
The disadvantages of the No. '067 mold closing device have been avoided in large measure in the No. '598 mold closing device, but the improved operating reliability of the latter device has been purchased with substantially higher manufacturing costs.